Investigation of additive manufacturing methodology with mixed silver powder and SU-8 conductive ink for 3-D RF structures

In this paper, we propose a novel additive manufacturing methodology to realize arbitrary 3-D RF structures. It could be briefly summarized as in-plane printing, 3-D printing and electroplating. Firstly, commercial silver powder is mixed with negative-tone photoresist SU-8 to function as a novel conductive ink for three dimensional (3-D) printing. The basic characteristics of printed traces including minimum trace width and thickness are determined by surface profile measurement results using Dektak Stylus Profiler. Subsequently, the horizontal movement of nozzle is optimized to ensure a flat surface with desired thickness. Since SU-8 is added into the conductive ink, UV irradiation and hard bake could help solidify the 3-D structures for rapid prototyping. To further improve RF performance, a layer of copper thin film is electroplated to cover surface of conductive ink. A preliminary study for validation purpose is conducted based on the configuration of non-grounded co-planar waveguide (CPW). Its measured S-parameters confirm the efficacy of proposed manufacturing methodology, which provides a promising solution and paves the way for designing 3-D RF structures.